Combustion engines based on Otto engines are generally operated with fuel consisting of hydrocarbons of fossil fuels on the basis of refined petroleum. Ethanol that is increasingly produced from re-growing natural resources (plants) or another alcohol is added to this fuel in different mixture ratios. In the United States and Europe a mixture of 70-85% ethanol and 15-30% gasoline are used under the trade name E85. The combustion engines are construed in such a way that they can be operated with pure gasoline as well as with mixtures up to E85; this is called ‘flex-fuel-operation’.
For an economical operation with a low pollutant emission at a simultaneously high engine performance and good starting behavior the operating parameters in the flex-fuel-operation have to be adapted to the present fuel mixture. A stoichiometric air/fuel ratio is for example present at 14.7 weight proportions of air per proportion of gasoline, but an air percentage of 9 weight proportions has to be adjusted when using pure ethanol. Furthermore the ignition angle of the combustion engine has to be adjusted to the mixture proportions for an optimal combustion.
Due to the different evaporation characteristics of ethanol and gasoline different enhancement factors have to be predefined at the start of the combustion engine depending on the mixture proportion. The knowledge of the present fuel mixture proportion is therefore of extreme importance for the operation of the combustion engine.
DE 41 17 440 C2 describes a procedure for an adaptive adjusting of an air/fuel mixture for considering fuel characteristics during the operation of a combustion engine, which provides a lambda regulator, which emits a regulating factor RF, and which provides an adaptation integrator, which emits an adaptation factor AF with a variable adaptation speed, which influences not only the regulating factor RF but also the adjustment of the air/fuel mixture. Thereby a checking of whether the lambda-regulating-deviation-amplitude exceeds a first threshold is provided, and, if that is the case, the adaptation speed is adjusted to a higher value so long until a preset condition is fulfilled, according to which it is switched back to a low adaptation speed. The underlying procedure is known as fuel adaptation.
The fuel adaptation allows a trouble-free operation of combustion engines, which can be operated with different fuels. Thus the injection time has to be extended by over 40% for example at a change from gasoline to a fuel mixture of 85% ethanol and 15% gasoline, in order to get the same lambda values in the exhaust gas. This is based on the different air demand for a stoichiometric combustion.
According to the procedure that is described in DE 41 17 440 C2 a corresponding adaptation intervention is carried out therefore. Because a correction of the injection times and therefore of the adaptation intervention that is very strong compared to balancing ageing influences or manufacturing influences has to be undertaken at a fuel exchange, the adaptation speed is significantly increased at the suggested procedure during a recognized fuel exchange.
The mixture proportion of the injected fuel can be implied from the adaptation intervention and the therefore resulting injection time or the fuel amount that has been injected into the combustion engine, whereupon further operating parameters of the combustion engine can be adjusted to the present fuel mixture.
The disadvantage of the described procedure is that at a required adaptation intervention into the lambda regulation it can not be surely determined anymore, whether the intervention is required because of ageing drifts and tolerances or because of a change of the fuel mixture proportions, thus whether the adaptation intervention has to be carried out by the mixture—or the fuel-adaptation. A corresponding attribution can be made with a certain probability based on distinction criteria, as for example the speed of the change or a refueling detection or a knock tendency.
But a residual uncertainty remains. If the system has unlearned once, thus if a change of the fuel mixture proportion has been interpreted falsely as a tolerance or an ageing drift and thus balanced correspondingly by a mixture adaptation, the error can only be detected and reversed very difficultly afterwards. Referring to the fuel injection it does not matter, whether the adaptation is carried out by the mixture adaptation or the fuel adaptation.
When changing the fuel mixture proportions further measures, as for example an adaptation of the ignition angle or a start enhancement, are necessary besides the adaptation of the fuel amount that has been injected into the combustion engine. These measures are not implemented in the described misinterpretation.
Further procedures, which are known from the patent literature, allow a conclusion about different characteristics of the used fuel, among others due to different mixture proportions of fossil fuel and alcohols, and a corresponding adaptation of the operating parameters of the combustion engine.
Thus DE 29 52 073 A1 describes a procedure for optimizing the working cycle of a spark-ignited combustion engine, at which the drive data of the combustion engine, among others the actually relative angle position of the crankshaft (crank angle), is measured, send to an electronic control unit and then the ignition time and/or the injected fuel amount is correspondingly affected. In doing so it is provided to vary around an approximate threshold value of at least one of the variables of the ignition time and/or the injected fuel amount from working cycle to working cycle.
Besides the crank angle the currently indicated pressure or a variable that changes analogously with is furthermore measured. By doing so and by determining the piston position by the crank angle the averagely indicated pressure or an analogous variable is calculated for each work stroke. The result of the calculated value of the averagely indicated pressure is registered and subsequently consecutive values are compared to each other. Thereby the variation of the variable is terminated for each operating status of the combustion engine and the present value of the variable is registered, as soon as the averagely indicated pressure reaches a maximum value.
The procedure also allows among others, to balance deviations of control parameters in the controlling of the combustion engine, which originate from the use of different fuels, as for example methanol, ethanol and gasoline.
A device for detecting the fuel characteristics is known from DE 38 33 123 A1, whereby the air amount that has been sucked in by the combustion engine and the air/fuel proportion in the exhaust gas are measured, whereby a significant fuel injection amount is calculated on the basis of the sucked in air amount and whereby the amount of the fuel that has to be inject is regulated correspondingly to the air/fuel proportion.
The device is characterized by pressure detection means for detecting the internal cylinder pressure, crankshaft detection means for detecting the crank angle of the combustion engine and a control device, which receives signals from the pressure detection means and the crank angle detection means and which calculates an effective fuel value Q of the fuel in an ignition cycle on the basis of the internal cylinder pressure P (θ) at a crank angle θ in the compression- and expression-strokes of an ignition cycle, the crank angle and the cylinder capacity V(θ), and which determines an effective combustion value K or a lower fuel value Hu of the fuel, whereby the characteristics of the fuel are determined by using at least the effective combustion value K or the lower fuel value Hu or the proportion (Ti/Hu) of the duration Ti of a fuel injection impulse to the lower fuel value Hu.
It is the task of the invention, to provide a procedure, which allows the determination of the proportion of components of a fuel mixture.